The design of radio frequency (RF) circuits requires careful attention to containment of the electrical and magnetic fields created at their operating frequencies. Instruments utilizing analog circuits at radio frequencies pose significant challenges in this area, as contrasted to digital circuit designs which require substantially less containment of radio frequencies due to the fact that digital circuits are far less sensitive to radiated interference. In analog circuits, isolation of one signal to another is vital to accurate circuit operation. Furthermore, escaping radiation can interfere with proper operation of nearby external electronics, such as radios, television receivers, and other devices.
Analog electronic instrumentation is typically encased within metal enclosures that are grounded to minimize radiation leakage to the exterior of the instrument and radiation cross coupling to other circuits. Openings in these enclosures require radiation gaskets, typically in the form of elongated metal spirals, braids, or flat spring forms that are compressed by pressure of a cover that bears against the gasket in only one direction. Such gaskets provide sealing to the cover along a single line extending across one cover surface. The dimensions and tolerances of the gaskets and covers are therefore critical to a good seal being established.
It is also well known that radio frequency interference can occur within the various conductive elements of printed circuitboards as radio frequency signals are transmitted through selected traces. Guard traces are typically provided alongside such traces to minimize such interference. Signal traces in base circuitboards, used to interconnect modular RF signal circuits, are a potential source of radiation leakage in such instrumentation.
The present invention was designed to maximize the exterior shielding of analog electronic circuits by improvement of the gasket technology used to prevent leakage of radiation from the interior operating environment of the circuits. It is directed specifically to the physical characteristics of a gasket used within an open slot to grip and hold a projecting edge of a wall forming part of a shielding structure, such as a circuitboard enclosure. The gasket is formed from an elongated strip of spring metal folded upon itself. The gasket engages and wraps about the edges of the wall edge received within the slot and frictionally engages both opposed inner slot surfaces and the wall received therein. The resilient gasket adapts to surface irregularities in the metal wall and slot surfaces.